The present invention relates to a new class of metallocene compounds, to a catalyst for the polymerisation of olefins containing them and to a polymerisation process carried out in the presence of said catalyst. The invention also relates to the corresponding ligands useful as intermediates in the synthesis of said metallocene compounds, as well as to processes for preparing said ligands and said metallocene compounds.
Metallocene compounds with two cyclopendadienyl groups are known as catalyst components for the polymerisation of olefins.
European Patent 0 129 368, for instance, describes the polymerisation of olefins in the presence of a bis-cyclopentadienyl co-ordination complex containing a transition metal. The two cyclopentadienyl groups can be linked by a bridging group, which is generally a divalent radical containing one or more carbon atoms or heteroatoms.
Also known are bridged metallocene compounds wherein the cyclopentadienyl moiety is condensed to one aromatic or non aromatic ring, the cyclopentadienyl moieties being linked by an ethylene bridge.
For example, European Patent Application EP-0 891 011 describes a process for the preparation of ethylene-based polymers in the presence of ethylenebis(4,7-dimethyl-1-indenyl)zirconium dichloride. The polymers obtained are endowed with low molecular weight. Moreover, the manufacture of ethylene-bridged metallocenes involves the use of the carcinogenic 1,2-dibromoethane.
As regards metallocenes having two equally substituted indenyl groups linked by a bridging group longer than two carbon atoms, only a few compounds have been disclosed.
For example, EP-A-0 399 348 and EP-A-0 459 320 describe the polymerisation of ethylene in the presence of propylenebis(1-indenyl)zirconium dichloride. Although the polyethylene obtained has industrially acceptable molecular weight, the metallocene used in the polymerisation process has low polymerisation activity.
W. A. Herrmann et al. in Angew. Chem. Int. Ed. Engl. 28 (1989), No. 11, describes the use of metallocenes containing two indenyl groups linked by a 1,2-bis(dimethylsilyl)ethane group for the polymerisation of olefins. Although completely inactive toward propylene, an activity toward ethylene was observed. However, there are no data reported about the molecular weight of the polymers.
It would be desirable to find carbon-bridged metallocenes which, when used in catalysts for the polymerisation of olefins, are suitable for the preparation of polyolefins, with the advantage of having higher polymerisation activities and of yielding polymers having improved molecular weights. It would also be desirable to avoid using the carcinogenic 1,2-dibromoethane used for the preparation of metallocenes.
A novel class of metallocene compounds has now unexpectedly been found which has two identical indenyl ligands which are linked to one another by a bridging group longer than an ethylene radical and which can advantageously be used as catalyst components for the polymerisation of olefins.
According to a first aspect, the present invention provides a metallocene compound of the formula (Ia): 
wherein
R1, same or different from each other, are C1-C20-alkyl, C3-C20-cycloalkyl, C2-C20-alkenyl, C6-C20-aryl, C7-C20-alkylaryl or C7-C20-arylalkyl radicals, optionally containing silicon or germanium atoms, and optionally two adjacent R1 substituents can form a ring comprising from 5 to 8 carbon atoms;
R2, same or different, are hydrogen atoms, C1-C20-alkyl, C3-C20-cycloalkyl, C2-C20-alkenyl, C6-C20-aryl, C7-C20-alkylaryl, C7-C20-arylalkyl, NR32, PR32, AsR32, OR3, SR3 or SeR3 radicals, optionally containing silicon, germanium or halogen atoms; and optionally two adjacent R2 or R3 substituents can form a ring comprising from 5 to 8 carbon atoms;
M is an atom of a transition metal selected from those belonging to group 3, 4, 5, 6 or to the lanthanide or actinide groups in the Periodic Table of the Elements (new IUPAC version),
Mxe2x80x2 is an atom of a transition metal selected from those belonging to group 3 or to the lanthanide or actinide groups in the Periodic Table of the Elements (new IUPAC version),
X, same or different, is a monoanionic ligand, such as a hydrogen atom, a halogen atom, an R4, OR4, OSO2CF3, OCOR4, SR4, NR42 or PR42 group, wherein the substituents R4 are a C1-C20-alkyl, C3-C20-cycloalkyl, C2-C20-alkenyl, C6-C20-aryl, C7-C20-alkylaryl or C7-C20-arylalkyl radical, optionally containing silicon or germanium atoms;
and optionally the six-membered rings of the compounds of formula (Ia) and (Ib) are perhydrated;
q is an integer from 3 to 5;
n is an integer from I to 4. when the six-membered rings of the compound of formula (Ia) are not perhydrated, and is an integer of from 0 to 4, when the six-membered rings of the compound of formula (Ia) are perhydrated as well as in the compound of formula (Ib);
p is an integer from 0 to 3, being equal to the oxidation state of the metal M minus two.
The transition metal M in compound of formula (Ia) is preferably selected from the group consisting of titanium, zirconium, hafnium, yttrium and scandium.
Non limiting examples belonging to this class are:
1,3-propandiylbis(4-methyl-1-indenyl)zirconium dichloride and dimethyl,
1,3-propandiylbis(5-methyl-1-indenyl)zirconium dichloride and dimethyl,
1,3-propandiylbis(6-methyl-1-indenyl)zirconium dichloride and dimethyl,
1,3-propandiylbis(4,7-dimethyl-1-indenyl)zirconium dichloride and dimethyl,
1,4-butandiylbis(4,7-dimethyl-1-indenyl)zirconium dichloride and dimethyl,
1,5-pentandiylbis(4,7-dimethyl-1-indenyl)zirconium dichloride and dimethyl,
1,6-hexandiylbis(4,7-dimethyl-1-indenyl)zirconium dichloride and dimethyl,
1,3-propandiylbis(4,7-diethyl-1-indenyl)zirconium dichloride and dimethyl,
1,4-butandiylbis(4,7-diethyl-1-indenyl)zirconium dichloride and dimethyl,
1,5-pentandiylbis(4,7-diethyl-1-indenyl)zirconium dichloride and dimethyl,
1,6-hexandiylbis(4,7-diethyl-1-indenyl)zirconium dichloride and dimethyl,
1,3-propandiylbis(4,7-diisopropyl-1-indenyl)zirconium dichloride and dimethyl,
1,4-butandiylbis(4,7-diisopropyl-1-indenyl)zirconium dichloride and dimethyl,
1,5-pentandiylbis(4,7-diisopropyl-1-indenyl)zirconium dichloride and dimethyl,
1,6-hexandiylbis(4,7-diisopropyl-1-indenyl)zirconium dichloride and dimethyl,
1,3-propandiyl(4,7-diisopropyl-1-indenyl)(4-isopropyl-1-indenyl)zirconium dichloride and dimethyl,
1,4-butandiyl(4,7-diisopropyl-1-indenyl)(4-isopropyl-1-indenyl)zirconium dichloride and dimethyl,
1,5-pentandiyl(4,7-diisopropyl-1-indenyl)(4-isopropyl-1-indenyl)zirconium dichloride and dimethyl,
1,6-hexandiyl(4,7-diisopropyl-1-indenyl)(4-isopropyl-1-indenyl)zirconium dichloride and dimethyl,
1,3-propandiylbis(4,7-dimethyl-1-tetrahydroindenyl)zirconium dichloride and dimethyl,
1,3-propandiylbis(1-tetrahydroindenyl)zirconium dichloride and dimethyl,
1,4-butandiylbis(4,7-dimethyl-1-tetrahydroindenyl)zirconium dichloride and dimethyl,
1,4-butandiylbis(1-tetrahydroindenyl)zirconium dichloride and dimethyl,
1,5-pentandiylbis(4,7-dimethyl-1-tetrahydroindenyl)zirconium dichloride and dimethyl,
1,5-pentandiylbis(1-tetrahydroindenyl)zirconium dichloride and dimethyl,
1,6-hexandiylbis(4,7-dimethyl-1-tetrahydroindenyl)zirconium dichloride and dimethyl,
1,6-hexandiylbis(1-tetrahydroindenyl)zirconium dichloride and dimethyl,
1,3-propandiylbis(4,7-diethyl-1-tetrahydroindenyl)zirconium dichloride and dimethyl,
1,4-butandiylbis(4,7-diethyl-1-tetrahydroindenyl)zirconium dichloride and dimethyl,
1,5-pentandiylbis(4,7-diethyl-1-tetrahydroindenyl)zirconium dichloride and dimethyl,
1,6-hexandiylbis(4,7-diethyl-1-tetrahydroindenyl)zirconium dichloride and dimethyl,
1,3-propandiylbis(4,7-diisopropyl-1-tetrahydroindenyl)zirconium dichloride and dimethyl,
1,4-butandiylbis(4,7-diisopropyl-1-tetrahydroindenyl)zirconium dichloride and dimethyl,
1,5-pentandiylbis(4,7-diisopropyl-1-tetrahydroindenyl)zirconium dichloride and dimethyl,
1,6-hexandiylbis(4,7-diisopropyl-1tetrahydroindenyl)zirconium dichloride and dimethyl,
1,3-propandiylbis(4,7-ditrimethylsilyl-1-tetrahydroindenyl)zirconium dichloride and dimethyl,
1,4butandiylbis(4,7-ditrimethylsilyl-1-tetrahydroindenyl)zirconium dichloride and dimethyl,
1,5-pentandiylbis(4,7-ditrimethylsilyl-1-tetrahydroindenyl)zirconium dichloride and dimethyl,
1,6-hexandiylbis(4,7-ditrimethylsilyl-1-tetrahydroindenyl)zirconium dichloride and dimethyl,
1,3-propandiylbis(4-methyl-1-indenyl)yttrium bistrimethylsilylmethyl,
1,3-propandiylbis(5-methyl-1-indenyl)yttrium bistrimethylsilylmethyl,
1,3-propandiylbis(6-methyl-1-indenyl)yttrium bistrimethylsilylmethyl,
1,3-propandiylbis(4,7-dimethyl-1-indenyl)yttrium bistrimethylsilylmethyl,
1,4-butandiylbis(4,7-dimethyl-1-indenyl)yttrium bistrimethylsilylmethyl,
1,5-pentandiylbis(4,7-dimethyl-1-indenyl)yttrium bistrimethylsilylmethyl,
1,6-hexandiylbis(4,7-dimethyl-1-indenyl)yttrium bistrimethylsilylmethyl,
1,3-propandiylbis(4,7-dimethyl-1-indenyl)scandium bistrimethylsilylmethyl,
1,4-butandiylbis(4,7-dimethyl-1-indenyl)scandium bistrimethylsilylmethyl,
1,5-pentandiylbis(4,7-dimethyl-1-indenyl)scandium bistrimethylsilylmethyl,
1,6-hexandiylbis(4,7-dimethyl-1-indenyl)scandium bistrimethylsilylmethyl,
1,3-propandiyl(4,7-dimethyl-1-indenyl)(4-methyl-1-indenyl)scandium bistrimethylsilylmethyl,
1,4-butandiyl(4,7-dimethyl-1-indenyl)(4-methyl-1-indenyl)scandium bistrimethylsilylmethyl,
1,5-pentandiyl(4,7-dimethyl-1-indenyl)(4-methyl-1-indenyl)scandium bistrimethylsilylmethyl,
1,6hexandiyl1(4,7-dimethyl-1-indenyl)(4-methyl-1-indenyl)scandium bistrimethylsilylmethyl
Non-limiting examples belonging to the class of compounds of formula (Ib) are:
di[1,3-propandiylbis(4,7-dimethyl-1-indenyl)yttrium hydride];
di[1,4-butandiylbis(4,7-dimethyl-1-indenyl)yttrium hydride];
di[1,5-pentandiylbis(4,7-dimethyl-1-indenyl)yttrium hydride];
di[1,6-hexandiylbis(4,7-dimethyl-1-indenyl)yttrium hydride];
di[1,3-propandiylbis(4,7-dimethyl-1-indenyl)scandium hydride];
di[1,4-butandiylbis(4,7-dimethyl-1-indenyl)scandium hydride];
di[1,5-pentandiylbis(4,7-dimethyl-1-indenyl)scandium hydride];
di[1,6-hexandiylbis(4,7-dimethyl-1-indenyl)scandium hydride];
di[1,3-propandiyl(4,7-dimethyl-1-indenyl)(4-methyl-1-indenyl)scandium hydride];
di[1,4-butandiyl(4,7-dimethyl-1-indenyl)(4-methyl-1-indenyl)scandium hydride];
di[1,5-pentandiyl(4,7-dimethyl-1-indenyl)(4-methyl-1-indenyl)scandium hydride];
di[1,6-hexandiyl(4,7-dimethyl-1-indenyl)(4-methyl-1-indenyl)scandium hydride].
A particularly interesting class of metallocenes according to the invention is that of the compounds of the formula (Ia), wherein the transition metal M is zirconium, the X substituents are chlorine atoms or methyl groups, the substituents R2 are hydrogen atoms and q is 3. Still particularly preferred are those compounds in which n is 2 and the two R1 substituents are in position 4 and 7 on the indenyl moieties.
Non limiting examples of that class are:
1,3-propandiylbis(4,7-dimethyl-1-indenyl)zirconium dichloride and dimethyl,
1,3-propandiylbis(4,7-diethyl-1-indenyl)zirconium dichloride and dimethyl,
1,3-propandiylbis(4,7-diisopropyl-1-indenyl)zirconium dichloride and dimethyl,
1,3-propandiylbis(4,7ditertbutyl-1-indenyl)zirconium dichloride and dimethyl,
1,3-propandiylbis(4,7-di-n-butyl-1-indenyl)zirconium dichloride and dimethyl,
1,3-propandiylbis(4,7-dicyclopropyl-1-indenyl)zirconium dichloride and dimethyl,
1,3-propandiylbis(4,7-dicyclobutyl-1-indenyl)zirconium dichloride and dimethyl,
1,3-propandiylbis(4,7-dicyclopentyl-1-indenyl)zirconium dichloride and dimethyl,
1,3-propandiylbis(4,7-dicyclohexyl-1-indenyl)zirconium dichloride and dimethyl,
1,3-propandiylbis(4,7-diphenyl-1-indenyl)zirconium dichloride and dimethyl,
1,3-propandiylbis(4,7-ditrimethylsilyl-1-indenyl)zirconium dichloride and dimethyl,
1,3-propandiylbis(4,7-ditrimethylgermilyl-1-indenyl)zirconium dichloride and dimethyl.
According to another aspect of the present invention there is provided a class of ligands of formula (II): 
wherein
R1, R2, n and q have the meaning as reported above.
The two double bonds of the cyclopentadienyl ring of the ligands of formula (II) can be in any of the allowed positions.
The aforementioned compounds of formula (II) are particularly useful as ligands for the preparation of the metallocene compounds of formula (Ia) and (Ib).
An advantageous class of ligands according to the present invention corresponds to formula (II), wherein R2 are hydrogen atoms and q is 3.
Non limiting examples of this class of ligands are:
1,3-propandiylbis(4,7-dimethyl-1-indenyl),
1,3-propandiylbis(4,7-diethyl-1-indenyl),
1,3-propandiylbis(4,7-diisopropyl-1-indenyl),
1,3-propandiylbis(4,7-ditertbutyl-1-indenyl),
1,3-propandiylbis(4,7-di-n-butyl-1-indenyl),
1,3-propandiylbis(4,7-dicyclopropyl-1-indenyl),
1,3-propandiylbis(4,7-dicyclobutyl-1-indenyl),
1,3-propandiylbis(4,7-dicyclopentyl-1-indenyl),
1,3-propandiylbis(4,7-dicyclohexyl-1-indenyl),
1,3-propandiylbis(4,7-ditrimethylsilyl-1-indenyl),
1,3-propandiylbis(4,7-ditrimethylgermyl-1-indenyl).
According to a further aspect of the present invention there is provided a process for the preparation of ligands of formula (II) comprising the following steps:
contacting a compound of formula (III): 
and its double bond isomers, wherein
R1 and n have the meaning as reported above, with a compound of general formula (CR2)qZ2, wherein R2 and q are defined as above, and Z is a halogen atom, in the presence of a base, to form a compound of formula (II).
As to the structural bridge (CR2)q in the above ligands, R2 and q have the meaning as defined above.
Non limiting examples of bases used to form the compound of formula (II) are hydroxides and hydrides of alkali- and earth-alkali metals, metallic sodium and potassium and organometallic lithium salts. Preferably, methyllithium or n-butyllithium is used.
Non limiting examples of compounds of general formula (CR2)qZ2 are 1,6-dibromohexane, 1,5-dibromopentane, 1,4-dibromobutane and 1,3-dibromopropane. Most preferably, 1,3-dibromopropane is used.
The synthesis of the above bridged ligands of formula (II) is preferably carried out by adding a solution of an organic lithium compound in an apolar solvent to a solution of the compound (III) in an aprotic polar solvent. The thus obtained solution containing the compound (III) in the anionic form is then added to a solution of the compound of formula (CR2)qZ2 in an aprotic polar solvent. The bridged ligand can be finally separated by conventional general known procedures.
Not limiting examples of aprotic polar solvents which can be used in the above process are tetrahydrofurane, dimethoxyethane, diethylether, toluene and dichloromethane. Not limiting examples of apolar solvents suitable for the above process are pentane, hexane and benzene.
During the whole process, the temperature is preferably kept between xe2x88x92180xc2x0 C. and 80xc2x0 C., and more preferably between xe2x88x9220xc2x0 C. and 40xc2x0 C.
A still further aspect of the present invention is a process for the preparation of the metallocene compounds of formula (Ia), obtainable by contacting the ligand of formula (II) as described above, with a compound capable of forming a corresponding dianionic compound thereof and thereafter smith a compound of formula MXp+2, wherein M, X and p have the meanings as defined above.
The compound able to form said dianion is selected from the group consisting of hydroxides and hydrides of alkali- and earth-alkali metals, metallic sodium and potassium, and organometallic lithium salts, and preferably said anion is n-butyllithium.
Non-limiting examples of compounds of formula MXp+2 are titanium tetrachloride, zirconium tetrachloride and hafnium tetrachloride. Preferably, zirconium tetrachloride is used.
The metallocene compounds of formula (Ia) can be prepared by first reacting the bridged ligands of formula (II), prepared as described above, with a compound able to form a delocalized anion on the cyclopentadienyl rings, and thereafter with a compound of formula MXp+2, wherein M and the substituents X are defined as above.
More specifically, said bridged ligands of formula (II) are dissolved in an aprotic polar solvent and to the obtained solution is added a solution of an organic lithium compound in an apolar solvent. The thus obtained anionic form is separated, dissolved in an aprotic polar solvent and thereafter added to a suspension of the compound MXp+2 in an aprotic polar solvent. At the end of the reaction, the solid product obtained is separated from the reaction mixture by techniques commonly used in the state of the art. Non limiting examples of aprotic polar solvents suitable for the above reported processes are tetrahydrofurane, dimethoxyethane, diethylether, toluene and dichloromethane. Non limiting examples of apolar solvents suitable for the above process are pentane, hexane and benzene.
During the whole process, the temperature is preferably kept between xe2x88x9280xc2x0 C. and 80xc2x0 C., and more preferably between xe2x88x9220xc2x0 C. and 40xc2x0 C.
A particularly convenient method for preparing the metallocene compounds of formula (Ia) and (Ib), in which the two six-membered rings of the indenyl groups are perhydrated, i.e. all carbon atoms of the six-membered ring of the indenyl radical are saturated, is the hydrogenation reaction of the corresponding metallocene compounds in which both indenyl groups are selected from the groups of formula (III). The hydrogenation reaction is carried out in a solvent, such as CH2Cl2, in the presence of a hydrogenation catalyst, such as PtO2, and hydrogen. The hydrogen pressures are preferably comprised between 1 and 100 bar, and the temperatures are preferably comprised betweenxe2x88x9250 and 50xc2x0 C.
When at least one X substituent in the metallocene compound of formula (I) is different from halogen, it is necessary to substitute at least one substituent X in the obtained metallocene with at least another substituent different from halogen. Such a substitution reaction is carried out by methods known in the state of the art. For example, when the substituents X are alkyl groups, the metallocenes can be reacted with alkylmagnesium halides (Grignard reagents) or with lithiumalkyl compounds.
According to another embodiment, when in formula (Ia) the X groups have the meaning of xe2x80x94R4, as defined above, the metallocenes of the invention can be obtained by reacting directly a ligand of formula (II) with at least one molar equivalent of a compound of formula MXs, in the presence of at least (p+2) molar equivalents of a suitable alkylating agent, wherein R4, M and X have the meaning reported above and s is an integer corresponding to the oxidation state of the metal M and ranges from 3 to 6. Said alkylating agent can be an alkaline or alkaline-earth metal, such as LiR4 or MgR42, or a Grignard reagent, such as R4MgCl or R4MgBr, as described in WO 99/36427.
During the whole process, the temperature is preferably kept between xe2x88x92180xc2x0 C. and 80xc2x0 C., and more preferably between xe2x88x9220xc2x0 C. and 40xc2x0 C.
According to a still further aspect of the present invention it is provided a process for the preparation of metallocene compounds of formula (Ib), comprising the following steps:
a) contacting a compound of formula (II) as defined above with a base selected from hydroxides and hydrides of alkali- and earth alkali metals, metallic sodium and potassium and organic lithium compounds, wherein the mole ratio between said base and the compound of formula (II) is at least 2.
b) contacting the product obtained under a) with a compound of formula (IV) Mxe2x80x2X3, Mxe2x80x2 being defined as above, and X is a halogen atom, in the presence of a polar aprotic solvent selected from dimethoxyethane, diethylether, tetrahydrofurane, toluene and dichloromethane;
c) treating the obtained product with a compound of formula Mxe2x80x3CH(TMS)2 (TMS=trimethylsilyl), Mxe2x80x3 being an alkali metal, and subsequent
d) treating the product of step c) in a stream of hydrogen.
Preferably the base as used in step a) is n-butyllithium. More specifically, said bridged ligands of formula (II) are dissolved in an aprotic polar solvent and to the obtained solution is added a solution of an organic lithium compound in an apolar solvent. The thus obtained anionic form is separated, dissolved in an aprotic polar solvent and thereafter added to a suspension of the compound Mxe2x80x2X3 in an aprotic polar solvent. At the end of the reaction, the solid product obtained is separated from the reaction mixture by techniques commonly used in the state of the art. Non limiting examples of aprotic polar solvents suitable for the above reported processes are tetrahydrofurane. dimethoxyethane, diethylether, toluene and dichloromethane. Preferably the polar aprotic solvent used in step b) is tetrahydrofurane.
Preferably the compound of formula (IV) is ScCl3 or YCl3.
Preferably the compound of formula Mxe2x80x3CH(TMS)2 is LiCH(TMS)2, NaCH(TMS)2 and KCH(TMS)2. Most preferably, LiCH(TMS)2 is used.
During the whole process, the temperature is preferably kept between xe2x88x92180xc2x0 C. and 80xc2x0 C., and more preferably between xe2x88x9220xc2x0 C. and 40xc2x0 C.
The metallocene compounds of the present invention can conveniently be used as catalyst components for the polymerisation of olefins.
Thus, according to a still further aspect of the present invention there is provided a catalyst for the polymerisation of olefins, obtainable by contacting:
(A) a metallocene compound of formula (Ia), and
(B) an alumoxane and/or a compound capable of forming an alkyl metallocene cation.
The alumoxane used as component (B) can be obtained by reacting water with an organo-aluminium compound of formula AIR53 or Al2R56, wherein the R5 substituents, same or different from each other, are hydrogen, C1-C20-alkyl, C3-C20-cycloalkyl, C6-C20-aryl, C7-C20-alkylaryl or C7-C20-arylalkyl. optionally containing silicon or germanium atoms In this reaction the molar ratio of Al/water is comprised between 1:1 and 100:1.
The molar ratio between aluminium and the metal of the metallocene is comprised between about 10:1 and about 20000:1, and preferably between about 100:1 and about 5000:1.
The alumoxanes used in the catalyst according to the invention are considered to be linear, branched or cyclic compounds containing at least one group of the type: 
wherein the R6 substituents, same or different, are hydrogen atoms, C1-C20-alkyl, C3-C20-cyclalkyl, C6-C20-aryl, C1-C20-alkylaryl or C7-C20-arylalkyl, optionally containing silicon or germanium atoms or are a xe2x80x94Oxe2x80x94Al(R6)2 group and, if appropriate, some R6 substituents can be halogen atoms.
In particular. alumoxanes of the formula: 
can be used in the case of linear compounds, wherein n is 0 or an integer from 1 to 40 and the R6 substituents are defined as above, or alumoxanes of the formula: 
can be used in the case of cyclic compounds, wherein n is an integer from 2 to 40 and the R6 substituents are defined as above.
Examples of alumoxanes suitable for use according to the present invention are methylalumoxane (MAO), tetra-(isobutyl)alumoxane (TIBAO), tetra-(2,4,4-trimethylpentyl)alumoxane (TIOAO), tetra-(2,3-dimethylbutyl)alumoxane (TDMBAO) and tetra-(2,3,3-trimethylbutyl)alumoxane (TTMBAO).
Particularly interesting cocatalysts are those described in WO 99/21899 in which the alkyl groups have specific branched patterns.
Non-limiting examples of aluminium compounds according to said PCT application are: tris(2,3,3-trimethyl-butyl)aluminium, tris(2,3-dimethyl-hexyl)aluminium, tris(2,3-dimethyl-butyl)aluminium, tris(2,3-dimethyl-pentyl)aluminium tris(2,3-dimethyl-heptyl)aluminium, tris(2-methyl-3-ethyl-pentyl)aluminium, tris(2-methyl-3-ethyl-hexyl)aluminium, tris(2-methyl-3-ethyl-heptyl)aluminium, tris(2-methyl-3-propyl-hexyl)aluminium, tris(2-ethyl-3-methyl-butyl)aluminium, tris(2-ethyl-3-methyl-pentyl)aluminium, tris(2,3-diethyl-pentyl)aluminium, tris(2-propyl-3-methyl-butyl)aluminium, tris(2-isopropyl-3-methyl-butyl)aluminium, tris(2-isobutyl-3-methyl-pentyl)aluminium, tris(2,3,3-trimethyl-pentyl)aluminium, tris(2,3,3-trimethyl-hexyl)aluminium, tris(2-ethyl-3,3-dimethyl-butyl)aluminium, tris(2-ethyl-3,3-dimethyl -pentyl)aluminium, tris(2-isopropyl-3,3-dimethyl-butyl)aluminium, tris(2-trimethylsilyl-propyl)aluminium, tris(2-methyl-3-phenyl-butyl)aluminium, tris(2-ethyl-3-phenyl-butyl)aluminium, tris(2,3-dimethyl-3-phenyl-butyl)aluminium, as well as the corresponding compounds wherein one of the hydrocarbyl groups is replaced by an hydrogen atom, and those wherein one or two of the hydrocarbyl groups are replaced by an isobutyl group.
Amongst the above aluminium compounds, trimethylaluminium (TMA), triisobutylaluminium (TIBAL), tris(2,4,4-trimethyl-pentyl)aluminium (TIOA), tris(2,3-dimethylbutyl)aluminium (TDMBA) and tris(2,3,3-trimethylbutyl)aluminium (TTMBA) are preferred.
In the catalyst used in the process according to the invention for the preparation of polyolefins, both the metallocene compound of the formula (Ia) and the alumoxane can be present as the product of the reaction with an organometallic aluminium compound of the formula AlR53 or Al2R56, in which the R5 substituents, same or different, are hydrogen atoms, halogen atoms, C1-C20-alkyl, C3-C20-cyclalkyl, C6-C20-aryl, C7-C20-alkylaryl or C7-C20-arylalkyl, optionally containing silicon or germanium atoms.
Non-limiting examples of aluminium compounds of the formula AlR5 3 or Al2R56 are: Al(Me)3, Al(Et)3, AlH(Et)2, Al(iBu)3, Al(iHex)3, Al(iOct)3, Al(C6H5)3, Al(CH2C6H5)3, Al(CH2CMe3)3, Al(CH2SiMe3)3, Al(Me)2iBu, Al(Me)2Et, AlMe(Et)2, AlMe(iBu)2, Al(Me)2iBu, Al(Me)2Cl, Al(Et)2Cl, AlEtCl2, Al2(Et)3Cl3, wherein Me=methyl, Et=ethyl, iBu=isobutyl, iHex=isohexyl, iOct=2,4,4-trimethyl-pentyl.
Non limiting examples of compounds able to form a metallocene alkyl cation are compounds of formula T+Dxe2x88x92, wherein T+ is a Brxc3x8nsted acid, able to give a proton and to react irreversibly with a substituent L of the metallocene of formula (Ia), and Dxe2x88x92 is a compatible anion, which does not co-ordinate, which is able to stabilise the active catalytic species which originates from the reaction of the two compounds and which is sufficiently labile to be able to be removed from an olefinic substrate. Preferably, the anion Dxe2x88x92 comprises one or more boron atoms. More preferably, the anion Dxe2x88x92 is an anion of the formula BAr(xe2x88x92)4, wherein substituents Ar, the same or different from each other, are aryl radicals such as phenyl, pentafluorophenyl, bis(trifluoromethyl)phenyl. Particularly preferred is the tetrakis-pentafluorophenyl borate. Furthermore, compounds of formula BAr3 can be suitably used.
The catalysts of the present invention are particularly suitable to be supported on inert carriers and used in the process of the present invention. This is obtained by depositing the metallocene (A) or the product of the reaction of the same with the component (B), or the component (B) and thereafter the metallocene (A), on supports such as for example silica, alumina, styrene-divinylbenzene copolymers, polyethylene or polypropylene.
The solid compound so obtained, in combination with further addition of the alkyl aluminium compound as such or pre-reacted with water, is usefully employed in gas phase polymerisation. Catalysts of the present invention are useful in the homo- and copolymerization reaction of olefins.
Therefore, a still further object of the present invention is a process for the polymerisation of olefins comprising the polymerisation reaction of at least an olefinic monomer in the presence of a catalyst as above described.
The catalysts of the present invention can be used in the homo-polymerisation reaction of olefins, preferably of ethylene for the preparation of HDPE. In ethylene polymerisation, the metallocenes of the invention show very good activities even when used in very low Al/Zr ratios.
A particular advantage of the metallocenes of the general formula (Ib) is their direct use in the polymerization process of olefins without the use of a cocatalyst.
Another interesting use of the catalysts according to the present invention is in the copolymerization of ethylene with alpha-olefins, such as propylene and 1-butene. In particular, the catalysts of the invention can be used for the preparation of LLDPE.
Suitable olefins to be used as comonomers comprise xcex1-olefins of the formula CH2xe2x95x90CHR7, wherein R7 is an alkyl radical having from 1 to 10 carbon atoms, and cycloolefins. Examples of these olefins are propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-esadecene, 1-octadecene, 1-eicosene, allylcyclohexene, cyclopentene, cyclohexene, norbornene and 4,6-dimethyl-1 -heptene.
The copolymers may also contain small proportions of units deriving from polyenes, in particular from straight or cyclic, conjugated or non conjugated dienes, such as 1,4-hexadiene, isoprene, 1,3-butadiene, 1,5-hexadiene and 1,6-heptadiene.
The units deriving from a-olefins of formula CH2xe2x95x90CHR7, from cycloolefins and/or from polyenes are present in the copolymers preferably in amounts ranging from 1% to 20% by mole.
The saturated copolymers can contain ethylene units and xcex1-olefins and/or non conjugated diolefins able to cyclopolymerise. The unsaturated copolymers can contain, together with the units deriving from the polymerisation of ethylene and xcex1-olefins, also small proportions of unsaturated units deriving from the copolymerization of one or more polyenes. The content of unsaturated units is preferably comprised between 0 and 5% by weight.
Suitable non conjugated diolefins able to cyclopolymerise comprise 1,5-hexadiene, 1,6-heptadiene and 2-methyl-1,5-hexadiene.
Non limiting examples of suitable polyenes are:
(i) polyenes able to give unsaturated units, such as:
linear, non-conjugated dienes, such as 1,4-hexadiene trans, 1,4-hexadiene cis, 6-methyl-1,5-heptadiene, 3,7-dimethyl-1,6-octadiene and 11-methyl-1,10-dodecadiene;
bicyclic diolefins, such as 4,5,8,9-tetrahydroindene and 6 and 7-methyl-4,5,8,9-tetrahydroindene;
alkenyl or alkyliden norbornenes, such as 5-ethyliden-2-norbornene, 5-isopropyliden-2-norbornene and exo-5-isopropenyl-2-norbornene;
polycyclic diolefins, such as dicyclopentadiene, tricyclo-[6,2,1,0]4,9-undecadiene and the 4-methyl derivative thereof;
(ii) non-conjugated diolefins able to cyclopolymerise, such as 1,5-hexadiene, 1,6-heptadiene and 2-methyl-1,5-hexadiene;
(iii) conjugated dienes, such as butadiene and isoprene.
Polymerisation processes according to the present invention can be carried out in gaseous phase or in liquid phase, optionally in the presence of an inert hydrocarbon solvent either aromatic (such as toluene), or aliphatic (such as propane, hexane, heptane, isobutane and cyclohexane).
The polymerisation temperature is preferably ranging from about 0xc2x0 C. to about 250xc2x0 C. In particular, in the processes for the preparation of HDPE and LLDPE, it is preferably comprised between 20xc2x0 C. and 150xc2x0 C. and, more preferably between 40xc2x0 C. and 90xc2x0 C., whereas for the preparation of the elastomeric copolymers it is preferably comprised between 0C and 200xc2x0 C. and, more preferably between 20xc2x0 C. and 100xc2x0 C.
The polymerisation pressure is ranging from 0,5 to 100 bar, preferably from 2 to 50 bar, and more preferably from 4 to 30 bar.
The molecular weight of the polymers can be also varied merely by varying the polymerisation temperature, the type or the concentration of the catalytic components or by using molecular weight regulators such as, for example, hydrogen.
The molecular weight distribution can be varied by using mixtures of different metallocenes, or carrying out the polymerisation in several steps at different polymerisation temperatures and/or different concentrations of the molecular weight regulator.
The polymerisation yields depend on the purity of the metallocene component of the catalyst. Therefore, in order to increase the yields of polymerisation, metallocenes are generally used after a purification treatment.
The components of the catalyst can be brought into contact before the polymerisation. The pre-contact concentrations are generally between 1 and 10 xe2x88x928 mol/l for the metallocene component (A), while they are generally between 10 and 10 xe2x88x928 mol/l for the component (B). The pre-contact is generally effected in the presence of a hydrocarbon solvent and, if appropriate, of small quantities of monomer. The pre-contact time is generally comprised between 1 minute and 24 hours.
The following examples are given to illustrate and not to limit the invention.
The following abbreviations are used:
THF=tetrahydrofuran
NaOEt=sodium ethoxide
BuLi=butyllithium
MeOH=methanol
EtOH=ethanol
KH=potassium hydride
TMSCl=trimethylsilylchloride
PBDMI=1,3-bis(4,7-dimethyl-1 -indenyl)propane
All operations were performed under nitrogen by using conventional Schlenk-line techniques. Solvents were distilled from blue Na-benzophenone ketyl (Et2O), CaH2(CH2Cl2) or AliBu3(hydrocarbons). and stored under nitrogen. BuLi (Aldrich) was used as received.
The 1H-NMR analyses of the metallocenes were carried out on an AC200 Bruker spectrometer (CD2Cl2, referenced against the middle peak of the triplet of the residual CHDCl2 at 5.35 ppm). All NMR solvents were dried over P2O5 and distilled before use. Preparation of the samples were carried out under nitrogen using standard inert atmosphere techniques. The lanthanide hydrades and CHTMS2 alkyls were characterized in C6D6.
Synthesis of xcex1, xcex1xe2x80x2-o-Xylenyl-bis-4,7-dimethylindene
In a 250 ml round-bottom flask supplied with magnetic stirrer and dropping funnel were placed 14.4 g (0.1 mol) of 4,7-dimethylindene and 130 ml of THF. This reaction mixture was cooled down to xe2x88x9278xc2x0 C. with acetone/dry ice mixture and 62.6 ml of 1.6 molar BuLi solution in hexane were added dropwise. Then, the cooling bath was removed and the temperature of the reaction mixture was slowly elevated until room temperature. The obtained dark colored mixture was transformed into 250 ml dropping funnel and added dropwise during 1 h to the solution of 13.2 g (0.05 mol) of xcex1,xcex1xe2x80x2- dibromoxylene in 100 ml of THF under vigorous stirring. During all the addition procedure the temperature of the reaction mixture was stirred overnight. 10 ml of methanol were added and the solvents were removed under reduced pressure. The resulting solvent was suspended in 100 ml of hexane/CH2Cl2 (4:1) mixture and passed through silica gel using the same mixture as eluent. Then solvents were removed under reduced pressure and the resulting slightly yellow crystalline product was washed twice with small portions of cold ethanol and dried in vacuum. Yield: 78%. Purity: 95.6%. The desired product was determined by 1H-NMR spectroscopy.
The preparation of ethylene-bis(4,7-dimethyl-indenyl)zirconium dichloride EBDMIZrCl2 was carried out according to the method described in the European patent application EP-0 821 011. Ethylen-bis(indenyl)zirconium dichloride EBIZrCl2 was purchased from the Witco company.